Cryptography Reference
In-Depth Information
Figure 8.1
A compression function
f
.
Against this background, an iterated hash function
h
can then be constructed,
as illustrated in Figure 8.2. In this figure,
f
represents the compression function and
g
represents an output function.
5
The message
x
is padded to a multiple of
b
bits
and divided into a sequence of
nb
-bit message blocks
x
1
,...,x
n
. The compression
function
f
is then repeatedly applied, starting with an initial value (
IV
=
H
0
)and
the first message block
x
1
, and continuing with each new chaining value
H
i
and
successive message block
x
i
+1
1. After the last message block
x
n
has been processed, the final chaining value
H
n
is subject to the output function
g
, and the output of this function is the output of the iterated hash function
h
for
x
(i.e.,
h
(
x
)).
for
i
=1
,...,n
−
3
./
@)0?
?
?
Figure 8.2
An iterated hash function
h
.
Hence, an iterative hash function
h
for
x
=
x
1
x
2
...x
n
can be recursively
computed according to the following set of equations:
H
0
=
IV
5
It goes without saying that
g
can also be the identity function.
